TRAVERSE ACROSS LOWER STRATA OF MERIDIANI PLANUM LAYERED DEPOSITS

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TRAVERSE ACROSS LOWER STRATA OF MERIDIANI PLANUM
LAYERED DEPOSITS
Alan D. Howard Department of Environmental
Sciences University of Virginia Jeffrey M.
Moore NASA Ames
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General Concept

• We have explored only the top few meters of the
  gt800 m thick stack of layered sediment in the
  Meridiani Planum region
• These layered deposits have the greatest areal
  extent and the most informative regional context
  of all layered deposit sequences
• We argue that these deposits accumulated as a
  sedimentary wedge at the edge of a large sea or
  ocean during the Noachian and are thus the most
  likely deposits to have incorporated organic
  compounds indicative of development of life

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The Regional Context
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A prominent topographic platform interrupts the
northwestward slope of the gradual transition
from highlands to lowlands It occurs at
elevations from about 0 to -1600 m with a sharp
drop off to about -2000 m We provisionally call
this the Meridiani Bench
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The purple line encloses the Meridiani Bench and
separates the Cratered Highlands from the Arabia
Lowlands
Arabia Lowlands
M.B.
Cratered Highlands
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The blue area is underlain by layered sediments
of the Meridiani Planum portion of the Meridiani
Bench. These layered sediments include the
hematite-rich deposits being visited by the
Opportunity Rover as well as sulfate-rich
deposits. We suggest that the entire Meridiani
Bench, including the Meridiani Planum deposits,
are underlain by a sedimentary sequence of
sediments eroded from the Cratered highlands
extending into a former sea or ocean extending up
to at least -1500 m
MP
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Prominent valley networks are shown in Cyan.
They do not extend below about -1500 m White
arrows show the ULM outflow channel system that
formed subsequent to the landforms discussed
here The possibility of a high-level ocean or
sea in this region has also been suggested by
Edgett and Parker 1997, Fairen et al. 2003,
Fairen and Dohm 2004, and Clifford and Parker
2001
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• A topographic barrier may have created
  semi-enclosed conditions that encouraged
  evaporite deposition as part of the Meridiani
  Planum sequence.
• Mawrth Valles may have been excavated by
  overflows/density flows over this barrier.
• Later outflow channel floods have breached this
  barrier.

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• We do not have the space or time here to develop
  the supporting evidence for our scenario, but a
  paper is in preparation
• Even if we are wrong, the presence of a thick
  sequence of layered deposits, hematite, hydrated
  minerals, and sufates warrants further
  exploration
• Previous regional geologic investigations of the
  Meridiani region have been published by Hynek et
  al. 2002, Arvidson et al. 2003 and Edgett
  2005.
• Edgett compares the region to the terrestrial
  Colorado Plateau

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The Proposed Site

• The steep, 300-400 m scarp defining the
  northwestern edge of the Meridiani
  Planum/Meridiani Bench deposits exposes probably
  the most complete section of the lower portions
  of the sequence, complementing the examination of
  the higher beds by Opportunity
• We have suggested a site near 354E and 8N
  permitting a traverse across this scarp

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X marks the spot, the line is the NW scarp
X
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IR Mosaic of Landing Site Region 3 proposed
sites
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The Geologic Context

• Hynek et al. 2001 and Edgett 2005 have
  provided geologic context
• Two prominent units define the sedimentary
  sequence occurring here
• A lower set of beds which locally appears to
  incorporate fluvial channel deposits
• An upper sequence characterized by reticulate
  ridges of layered deposits

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X
PPlains-forming Unit RRidge-forming
Unit SScarp Forming Unit LLower Unit
(Edgett,2005)
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(Hynek et al., 2002)
X
CsCratered, Subdued CuCratered,
Undivided ILInterior Layered P1Plains,
Lower P2Plains, Upper PhPlains, Middle P3Etched
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Images of Region
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1 - E2200443
2 E2200081
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VIS mosaic showing locations of detailed MOC
images
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1 R1601540
Scarp in lower layered unit possibly traversable
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2 R1601540
In landing ellipse somewhat scabby texture
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3 R1601540
Upper ridged unit probably can be sampled at
various levels
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Landing site thermal intertias 200, about the
same as the Opportunity site
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Landing Site does not contain extensive exposures
of hydrated minerals
X
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A Possible Extended Mission Target

• The 70 km crater about 20 km to the west of the
  landing site contains some of the best exposures
  of rhythmically-layered sediment on Mars
• The issue is feasibility of descending into the
  crater and traversing the rough floor

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Landing Site Coordinates L1 354.029E
7.900N L2 353.975E 8.260N L3 354.545E
8.408N (listed in order of decreasing
priority) Regional Polygon Vertices 352.91E
8.64N 354.72E 8.49N 354.61E 7.95N 353.09E
7.25N
E
E is the potential extended mission target
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Landing site is within mantled portion of Arabia,
but detailed images show lots of rock exposures
X
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SummaryWhy Revisit Meridiani

• Meridiani (whether at our proposed site or
  elsewhere) contains probably the largest and best
  exposed layered deposits of probable fluvial or
  lacustrine origin on Mars.
• The Meridiani site occurs on a gradual transition
  from highlands to lowlands and thus provides
  abundant geologic context for interpretation of
  age and depositional environment.
• A strong case can be made that the Meridiani
  deposits were deposited into a large regional sea
  or ocean, either open or ice-covered.

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• It is likely that a site can be found in the
  Meridiani Planum region that
• Provides an adequate landing environment
• Provides close access to a thick sequence of the
  lower beds of the stratigraphic column
• Contains accessible traverses
• Contains low-energy fluvial or lacustrine
  depositional environments with abundant hydrated
  minerals and chemical precipitates
• Affords dust-free exposures

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Issues with Site

• Local steep slopes within the 20-km ellipses
• Small-scale roughness on portions of the landing
  sites
• Located in a partially mantled portion of Arabia
• May not be able to access rhythmically-bedded
  deposits within crater
• No extensive exposures of hydrated minerals seen
  so far

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X
Other potential landing site locations with thick
exposed sequences of Meridiani layered deposits
(arrows)
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• The next slide shows other potential traverse
  locations, shown on V037200003 (left) and
  V04881003 (right)

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